This section provides background information related to the present disclosure which is not necessarily prior art.
Large optics fabrication techniques are key enablers of lightweight space applications and high power laser systems, especially where the power is usually carried by large aperture beams to reduce the intensity. For both fields, technologies that have the flexibility to allow for freeform optics and complex alternating optics such as gratings are desirable. One example for useful freeform operations may involve correcting high order aberrations for traditionally built lenses. Another example is with contour phase plates (CPP) for inertial confinement fusion (ICF) laser systems, and combining optical functions for light-wave systems.
Existing technologies for producing large-scale optics with free form flexibility are diamond turning polishing and Magnetorheological Finishing (MRF). However, the diamond turning polishing technique provides limited surface quality with respect to optical grade. Furthermore, its laser damage resilience, without further surface treatment, may alter the surface morphology, and therefore is relatively low. MRF can produce a high quality surface but is time consuming to perform. Still further, the resulting maximal modulation of an optical function with MRF manufactured optic is limited by the small material removal and the spatial resolution that are achievable with MRF.
Uniform random nanostructured Silica may be used as an anti-reflective (AR) layer for high power laser systems with proven high laser-induced damage threshold. This nanostructured AR layer replaces traditional AR coating by introducing effectively the same refractive index at a thin layer near the substrate surface. This results from insensitivity of the wave to the specific features due to their subwavelength lateral scale as the wave reacts to the net weighted averaged refractive index. These nanostructured AR layers are fabricated using Reactive Ion Etching (RIE) resulting in a random rough surface with subwavelength features. This technique is limited to application of spatially uniform refractive index layer, where the feature-size distribution across the structure is being controlled by the etching reactant and exposure.
One particular method to create nano-sized metal particles on a substrate is by thermally de-wetting a thin metal layer. This procedure turns a portion of the metal layer into metal particles with size distribution controlled by the deposited thermal energy. In effect, the metal film melts and then balls up into liquid droplets on the surface, followed by the formation of metal nano-particles as these droplets cool and re-solidify.